Micro-mechanical polarization-based modulator

ABSTRACT

A micro-mechanical spatial light modulator for modulating a polarization state of an incident beam ( 20 ) comprises a plurality of rotatable elements. Each of the rotatable elements ( 170 ) comprises a plurality of structures ( 300 ). The structures are spaced apart at sub-wavelength distances relative to the wavelength of the incident beam ( 20 ). Each of the plurality of structures ( 300 ) exhibits an interaction with the polarization state of the incident beam. An actuator is coupled to each of the rotatable elements. The actuator is capable of controllably positioning the rotatable element to any two positions, and each of the positions has a corresponding polarization state. A substrate ( 110 ) supports each plurality of rotatable elements and houses each actuator.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to commonly-assigned U.S. patent application Ser. No.09/799,281, filed Mar. 5, 2001, entitled WIRE GRID POLARIZER, by Kurtzet al., the disclosure of which is incorporated herein.

FIELD OF THE INVENTION

This invention generally relates to spatial light modulators and inparticular relates to a polarization-based modulator comprising an arrayof micro-mechanical assemblies.

BACKGROUND OF THE INVENTION

Spatial light modulators have been adapted for use in a range of imagingapplications, particularly in projection and printing apparatus. Inoperation, a spatial light modulator array provides a pattern ofindividual light modulators, each modulator typically corresponding to apixel for representing a two-dimensional image. Light can be modulatedby modifying the incident light according to selective absorption,reflection, polarization state change, beam steering, diffraction,wavelength separation, and coherence modification. Typically, theinteraction of the light and modulator is enabled using electro-optic oracousto-optic materials, or a micro-mechanical structure, patterned witha series of addressing electrodes.

In particular, the liquid crystal display (LCD) is a widely used type ofspatial light modulator, which operates by the modulation of thepolarization state of incident light. LCDs are commonly used in laptopcomputer displays, pagers, and game displays, as well as in projectionand printing systems. LCD spatial light modulators are available in arange of types and may use any of a number of underlying technologies,including devices using nematic, twisted nematic, cholesteric, smectic,and vertically aligned liquid crystal molecules. LCDs are described innumerous patents, including for example, U.S. Pat. No. 4,688,897(Grinberg et al.); U.S. Pat. No. 5,039,185 (Uchida et al.); U.S. Pat.No. 5,652,667 (Kuragane); and U.S. Pat. No. 5,847,789 (Nakamura et al.).LCDs are also available in a wide range of sizes, from devices suited tomicro-displays to devices used for direct view laptops. LCD performancecharacteristics, such as response time, angular acceptance, contrast,and control voltages, vary depending on the device.

Spatial light modulators that alter the polarization state of incidentlight have also been constructed using lead lanthanum zirconium titanate(PLZT), as described in U.S. Pat. No. 4,707,081 (Mir), U.S. Pat. No.4,887,104 (Kitano et al.), and U.S. Pat. No. 5,402,154 (Shibaguchi etal.). While PLZT devices are robust relative to optical damagethresholds, these devices typically have modest modulation speeds (kHzrange), require high drive voltages, and have electro-optic responsecurves with significant hysteresis.

LCD and PLZT devices are suitable for many applications, but have anumber of inherent disadvantages, including relatively slow responsetimes (typically a few ms) and significant optical response variationsrelative to the angle of incidence. Most LCD modulators are unable toprovide both high modulation contrast and fast modulation speedssimultaneously. Modulation contrast not only varies with angle andwavelength, but can also be degraded by thermally induced stressbirefringence when exposed to the large light loads common to projectionapplications. In demanding applications using LCDs, the systems areoften enhanced through the use of carefully designed polarizationcompensators (for example see U.S. Pat. No. 4,701,028 (Clerc et al.) andU.S. Pat. No. 6,081,312 (Aminaka et al.), which boost contrast, but atthe cost of additional optics to the system.

One approach to providing spatial light modulators with improvedresponse time is to adapt micro-mechanical devices to this task. Thedigital micro-mirror device (DMD) from Texas Instruments, Dallas, Tex.,as disclosed in U.S. Pat. No. 5,061,049 (Hornbeck), is one such device,which modulates by beam steering the incident light relative to theimaging optics. Micro-mechanical gratings, including the grating lightvalve (GLV), disclosed in U.S. Pat. No. 5,311,360 (Bloom), and theconformal grating modulator, disclosed in U.S. Pat. No. 6,307,663(Kowarz), have been successfully developed. These gratings impart aphase pattern to the incident light, causing it to diffract whenmodulated. Both the micro-mirror and the grating modulators require theuse of a Schlieren type optical system, with blocking apertures orangular separation, to distinguish between the modulated andun-modulated light. Alternately, a spatial light modulator with rollingmicro-mechanical shutters is described in U.S. Pat. No. 5,233,459(Bozler et al), which either blocks or transmits the incident light,according to the control signals. As compared to the electro-optical oracousto-optical devices, the micro-mechanical modulators typicallyprovide a more uniform response, both within a device (from pixel topixel) and relative to the properties of the incident light (angle ofincidence, wavelength, etc.). The micro-mechanical optical modulatorsalso typically provide faster response times (On to Off, and visa-versa)than do many of the electro-optical devices. While these devices haveprovided some improvements in performance, there is room forimprovement. For example, DMD devices are capable of achieving higherspeeds, but are presently limited in achieving high resolution, andlimit the input light to a modest angular beam width (<10° or<F/3.0). Bycomparison, the GLV and related devices are generally limited to onedimensional structures, due to optical fill factor issues betweenadjacent rows.

While micro-mechanics have been applied to light modulation using beamsteering, diffraction, and beam blocking mechanisms, there are furtheropportunities to bring the advantages of micro-mechanical (MEMS)structures to the area of optical modulation. In particular, an improvedpolarization modulator could be designed, with potentially fasterresponse times and more uniform angular and wavelength responses ascompared to some of the conventional electro-optical devices.

Micro-mechanical structures, which might be adaptable to theconstruction of a micro-mechanical polarization modulator, have beendescribed, including motors, rotors, and mini-turbines. Exemplarystructures and manufacturing processes for micro-motors are discussed innumerous prior art patents, including U.S. Pat. No. 5,252,881 (Muller etal.), U.S. Pat. No. 5,710,466 and U.S. Pat. No. 5,909,069 (both to Allenet al.), and U.S. Pat. No. 5,705,318 (Mehregany et al.). Micro-motorshave been fabricated and tested on a scale as small as 60-100 μmdiameter, which is of a size appropriate for building a pixilatedspatial light modulator, although smaller motor diameters could beuseful. U.S. Pat. No. 5,459,602 (Sampsell) and U.S. Pat. No. 5,552,925(Worley) describe micro-motors that are adapted with revolving bladeshutters. Alternately, U.S. Pat. No. 6,029,337 (Mehregany et al.)describes a micro-motor structured to facilitate the creation of avariety of devices, including a micro-polygon scanner and micro-gratingoptical scanner. In particular, FIG. 4 of U.S. Pat. No. 6,029,337illustrates the concept of a rotating diffraction grating (long pitch(p>>λ)), mounted to a micro-motor, and used in an optical scanner. Thesedevices, operating at rotational speeds up to 50,000 rpm (1.2msec/rev.), can be used in optical systems for a variety ofapplications, including bar code scanners and laser printers.

However, U.S. Pat. No. 6,029,337 neither describes the design andconstruction of a micro-mechanical polarization spatial light modulator,nor anticipates the potential advantages of such a device and itsapplication within a modulation optical system. In particular, such adevice is necessarily fabricated with a surface structure that altersthe polarization state of the incident light in accordance with itrotational position. Traditionally, optical polarizers have beenconstructed with bulk materials, such as crystal calcite, or as thePolaroid type dye sheets with stretched polymers, or as optical thinfilms within glass substrates (U.S. Pat. No. 2,403,731 (MacNielle)), orfinally as aligned metallic needles embedded in a glass medium (U.S.Pat. No. 5,281,562 (Araujo et al.) and U.S Pat. No. 5,517,356 (Araujo etal.). Although these various types of polarizers are valuable in theirown right, they do not lend themselves to integration with amicro-mechanical structure. In particular, these types of polarizerstend to be both large in scale (millimeters and centimeters in extent)and use fabrication processes not conducive to the miniaturization.Furthermore, even if these polarizer types were fabricated on thesub-millimeter scale, they are not readily attached or integrated onto amicro-mechanical device.

Polarizers can however be manufactured with processes that lendthemselves to modern manufacturing techniques for miniaturization andpatterning. Furthermore, such polarizers can be manufactured for thevisible wavelength range, rather than the infra-red wavelength range,where such form-birefringent and form-dichroic structures werepreviously limited. Form-birefringent, all dielectric, sub-wavelengthstructures have been developed for use as polarization sensitivemirrors, polarizing beansplitters, and waveplates. In such structures, asub-wavelength grating structure is formed in a dielectric material,with various parameters, including the pattern, groove period, grooveprofile, and groove depth, determining the performance of the device. Asan example, the paper “Design considerations of form-birefringentmicro-structures”, I. Richter et al., Applied Optics, Vol. 34, No. 14,pp. 2421-2429, May 1995, discusses many of the design compromises andissues in the design of such structures.

Optical polarizers with sub-wavelength structures can also be designedand fabricated with mixed metal-dielectric structures. In particular,U.S. Pat. No. 6,122,103 (Perkins et al) and U.S. Pat. No. 6,243,199(Hansen et al) describe visible wavelength wire grid polarizers andpolarization beamsplitters fabricated from sub-wavelength metallic wiredeposited on a glass substrate. As compared to the all dielectricdevices, the wire grid devices typically provide greater differences inresponse (higher contrast) for the transmitted polarization vs. thereflected polarization. However, both the dielectric-form-birefringentpolarizers and the wire grid polarizers generally provide polarizationresponses that are generally uniform over extended wavelength ranges andlarge ranges of incident angles.

In general, the use of dielectric-form-birefringent polarizers and thewire grid polarizers has been applied to static optical devices, such aswaveplates, polarizers, and polarization beamsplitters, which reside ina pre-determined position within an optical system. Spatial lightmodulators, such as liquid crystal displays, may also exist within thesesystems, and provide the actual data input modulation. However, theoperation of such systems is then typically limited by the polarizationresponse of the liquid crystal displays, and the full polarizationresponse of the sub-wavelength structured polarizer is under utilized.If, on the other hand, the use of sub-wavelength structure polarizerswere applied to the construction of the modulator itself, the overallresponse of the optical systems could be improved. In particular, therehas been no attempt to adapt sub-wavelength structured optical retardersand polarizers in the construction of spatial light modulators usingmicro motors.

Thus it can be seen that there is an opportunity for a spatial lightmodulator that operates by polarization modulation, employingsub-wavelength structured optical polarizers controlled bymicro-mechanical actuators, which are preferably micro-mechanicalmicro-motors.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a spatial lightmodulator for modulating the polarization state of an incident beam.

Briefly, according to one aspect of the present invention amicro-mechanical spatial light modulator for modulating a polarizationstate of an incident beam comprises a plurality of rotatable elements.Each rotatable element comprises a plurality of structures. Thestructures are spaced apart within sub-wavelength distances relative tothe wavelength of the incident beam. Each of the plurality of structuresexhibits an interaction with the polarization state of the incidentbeam. A micro-motor is coupled to each of the rotatable elements. Themicro-motor is capable of controllably positioning the rotatable elementto at least two positions. Each position has a correspondingpolarization state. A substrate structure supports each of the pluralityof rotatable elements and houses each micro-motor.

A feature of the present invention is that it provides an array ofmicro-mechanical structures comprising sub-wavelength opticalpolarization modulators arranged in a two-dimensional array, whereineach modulator is independently actuated by a micro-mechanicalmicro-motor.

It is an advantage of the present invention that it provides a spatiallight modulator that is capable of providing uniform angular responsewith fast response times.

These and other objects, features, and advantages of the presentinvention will become apparent to those skilled in the art upon areading of the following detailed description when taken in conjunctionwith the drawings wherein there is shown and described an illustrativeembodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter of the present invention, itis believed that the invention will be better understood from thefollowing description when taken in conjunction with the accompanyingdrawings, wherein:

FIG. 1a shows a view in cross section of a modulation optical system,containing a spatial light modulator according to the present invention,showing its operation upon incident light;

FIG. 1b shows a view in cross section of an alternate modulation opticalsystem, containing an alternate spatial light modulator of the presentinvention, showing its operation upon incident light;

FIG. 2 is a plane view showing a portion of a micro-mechanical arrayaccording to the present invention;

FIG. 3 is an enlarged cross sectional side view showing a singlemicro-mechanical modulator component that corresponds to a single imagepixel;

FIG. 4 is a plane view showing the underlying structure of amicro-mechanical micro-motor used in a preferred embodiment;

FIG. 5 provides a perspective view of a polarization optical layerconstructed as a form-birefringent waveplate, which forms a portion ofthe micro-mechanical polarization modulator of the present invention;

FIGS. 6a and 6 b show the operation of the micro-mechanical modulatorand its interaction with an incident light beam for two polarizationstates;

FIG. 7 shows a perspective view of a prior art wire grid polarizer.

FIG. 8 shows a perspective view of a polarization optical layer with analternate construction as a wire grid polarizer; and

FIG. 9 shows a side view in cross section of a polarization opticallayer with an alternate construction as a subwavelength opticalstructure with stratified internal layers of different materials.

DETAILED DESCRIPTION OF THE INVENTION

The present description is directed in particular to elements formingpart of, or cooperating more directly with, apparatus in accordance withthe invention. It is to be understood that elements not specificallyshown or described may take various forms well known to those skilled inthe art.

Referring to FIG. 1a, a spatial light modulator array 50 according tothe present invention functions as an optical modulator which alters thepolarization state of incident light. Modulation optical system 10comprises a pre-polarizer 25, a polarization beamsplitter 30, spatiallight modulator array 50, polarization analyzer 35, and a projectionlens 70. Typically, projection lens 70 directs light to a distant targetplane (not shown) to form an image of the spatial light modulator array50. Modulation optical system 10 may comprise a portion of an electronicprojection system or an image printing system. However, modulationoptical system 10 may be applied to other uses, such as for example, anoptical character recognition system.

An incident light beam 20 originates from a light source (not shown),which for example may be an arc lamp (such as xenon or metal halide), ahalogen or incandescent lamp, one or more LEDs (light emitting diodes),or a laser. Typically the incident light beam 20 is modified and shapedby an illumination system (not shown), which may include condensingoptics, light homogenizers, such as fly's eye integrators, light pipes,fiber optic bundles, or kaleidoscopes. With the exception of the laser,these light sources typically emit un-polarized light, and thusmodulation optical system 10 is equipped with a pre-polarizer 25, whichdefines the preferred polarization state for incident light beam 20,while typically retro-reflecting light of the opposite polarizationstate back towards the light source. Additionally, a polarizationconverter may be used to selectively alter the light of the rejectedopposite polarization state to match the desired polarization state, andthen re-combine this light with larger flux.

Polarized light beam 21 is directed upon polarization beamsplitter 30,which splits this light into a transmitted polarized light beam 40 ofone polarization state, and a reflected light beam 37 of the oppositepolarization state in accordance to the properties of its internalpolarizing filter layer 32. For example, polarization beamsplitter 30may be a MacNielle type prism (reference U.S. Pat. No. 2,403,371) whichnominally transmits “p” polarized light and reflects “s” polarizedlight. Typically the “p” polarized transmitted light becomes thetransmitted polarized light beam 40 which is directed onto the lightmodulator 50, as the polarization contrast (Tp/Ts) for this transmittedlight is higher than the polarization contrast for the reflected light(Rs/Rp). This low contrast reflected light becomes reflected light beam37, which is generally directed out of the modulation optical system 10.Depending on the application and design, reflected light beam 37 may bedirected into a light trap, onto another light modulator, or recycledback to the light source.

As polarization beamsplitter 30 separates the incident light beamaccording to polarization, it can also function as the pre-polarizer formodulation optical system 10. In actuality, both pre-polarizer 25 andpolarization analyzer 35 are optional for use in modulation opticalsystem 10, with their inclusion dependent upon the system contrastspecification and the properties of the incident light (wavelength band,numerical aperture, innate polarization state, etc.). Both pre-polarizer25 and polarization analyzer 35 may be a stretched polymer dye sheetpolarizer (such as the original Polaroid polarizer, or more recently,the polarizer of U.S. Pat. No. 6,049,428), a wire grid polarizer(reference U.S. Pat. No. 6,122,103), a MacNielle type polarizationprism, or any one of several other types of appropriate opticalpolarizers. Depending on the polarizer used, the rejected polarizationstate light is either reflected or absorbed. On the other hand,polarization beamsplitter 30 cannot absorb the rejected polarizationstate light, but must reflect one state, and transmit the oppositestate, along directions separate both from each other and from theincident light. While polarization beamsplitter 30 may be of theMacNielle type, other polarization beamsplitter types may be included inmodulation optical system, including the PTIR prism (reference U.S. Pat.No. 5,912,762), the liquid prism (reference U.S. Pat. Nos. 4,544,237 and5,844,722), and the wire grid polarization beamsplitter (reference U.S.Pat. No. 6,243,199).

Using the construction provided in FIG. 1a for modulation optical system10, incident light beam 20 is transmitted through polarizationbeamsplitter 30, forming a transmitted polarized light beam 40(typically “p” state polarized), which is directed onto spatial lightmodulator array 50. Spatial light modulator array 50 then modulates thepolarized incident light beam 40 on a pixel by pixel basis in accordancewith the applied drive signal 51, by rotating the polarization state ofthe incident light. Drive signal 51 may be provided by a video board,raster image processor, or other data sources such as is well known inthe art. Relative to FIG. 1a, the modulated On-state 55 light is “s”polarized, and after reflection off spatial light modulator array 50,this light reflects off the internal polarizing filter layer 32 withinpolarization beamsplitter 30, and passes through polarization analyzer35 and projection lens 70. The unmodulated Off-state light is light thatremains “p” polarized. After reflection off of spatial light modulatorarray 50, this unmodulated “p” polarized Off-state light is transmittedthrough the internal polarizing filter layer 32 of polarizationbeamsplitter 30. Thus, the Off-state light is transmitted straightthrough polarization beamsplitter 30, such that it travels back alongthe optical path of incident light beam 20, and is generally directedback towards the light source.

The contrast between the modulated On state and unmodulated Off statelight is determined by the performance characteristics of both the lightmodulator and the polarization optics. For example, the modulationcontrast (On State/OffState) significantly depends on the residualamount of“s” state polarized light accompanying the Off state “p”polarized light. This residual “s” light can either be from leakagethrough the polarizing beamsplitter 30 or from incomplete rotation ofthe polarization vectors by spatial light modulator array 50. As thepolarization response of both the light modulator and the polarizationoptics vary with wavelength and angular width (numerical aperture), theamount of residual leakage light of the unwanted polarization islikewise dependent on these conditions. In some optical systems,polarization compensators (for example, reference U.S. Pat. No.5,375,006) are used to modify the polarization states of the transitinglight in a pre-determined fashion vs. space or angle, so that theoverall modulation contrast is increased. Additionally, depending on theperformance characteristics of the spatial light modulator array 50,light may also be modulated to provide gray scale resolution, by drivingthe polarization rotation to intermediate amounts, such that both “s”state and “p” state light emerge from the modulator in controlledamounts.

Referring to FIG. 2, there is shown a plane view of spatial lightmodulator array 50 of the present invention, comprising an orderedarrangement of micro-mechanical polarization modulators 100. Eachmodulator (or pixel) 100 can be individually actuated to one of at leasttwo angular positions (corresponding to ON and Off) in order to providea predetermined polarization modulation to an incident light beam. Itshould be noted that for simplicity of illustration FIG. 2 shows only aportion of spatial light modulator array 50 containing merely 24modulators 100, arranged in a 4×6 matrix. In a practical spatial lightmodulator array 50 for projection or printing use, for example, spatiallight modulator array 50 might comprise an array of 1024×640 modulators100. Each modulator 100 comprises both an optic 200, shown in moredetail in FIG. 3, with polarization optical properties, and amicro-mechanical actuator to provide controlled motion in accordancewith the drive signal 51.

In a preferred embodiment, actuation of each modulator 100 is controlledby a micro-motor 105 as is shown in the cross-section view of FIG. 3 andin the plane view of FIG. 4. Micro-motor 105 as shown in FIG. 3 is abasic type of electrostatic micro-motor such as that disclosed in FIGS.2 and 3 of U.S. Pat. No. 5,252,881 (Muller et al.) This design allowsconstruction of micro-motor 105 having dimensions on the order of 200microns or smaller as viewed in the flat plane view of FIG. 4.Micro-motor 105 is constructed on a substrate 110, typically polysiliconor other suitable material, with an intermediate layer 112 provided asan insulating layer. Intermediate layer 112 comprises a complex patternof several layers, including both circuitry and insulating layers, toprovide pixel/motor addressing, so that control signals can beintroduced. Micro-motor 105 comprises a rotor 160 that rotates about acentral flange bearing 130. A lower flange 132 and an upper flange 134are provided to retain rotor 160 in place. An additional layer, mask136, can be provided atop flange bearing 130. Stators 140, energizedthrough stator leads 144, provide the electrostatic charge to statorpoles 142 for driving rotation of rotor 160, with an air gap 120separating stator poles 142 from rotor poles 162. As is shown in FIG. 4,rotor 160 comprises a number of rotor poles 162. An insulating layer 166can be used to isolate a ground plane 164 from the stator leads 144.

Relative to spatial light modulator array 50, which comprises amultitude of modulators or pixels 100, each of these modulators 100comprise both a micro-motor 105 and an optic 200, with a structure ofoptical layers 170. In the case of FIG. 3, these optical layers 170comprise mask 136, polarization optical layer 176, and reflective layer174. Polarization optical layer 176 and reflective layer 174 are mountedon top of a support 172, and support 172 is attached to rotor 160.Polarization optical layer 176 contains the birefringent polarizingstructures, as described below. Reflective layer 174 is disposed betweenpolarization optical layer 176 and support 172. Notably, support 172 isscaled to overhang rotor 160 and stator 140, in order to maximize theoptical fill factor provided by modulator optical system 10. For thespatial light modulator array 50 of FIG. 2, in which each of the pixels100 have optical layers covering a nominally circular area, while thepixels are laid out in a square grid, the maximal optical fill factor Fis ˜π/4˜0.78. The fill factor would be further reduced by the exposedarea of the flange bearing 130 and the designed gap between pixels in anarray modulator device. Ideally, the modulator might be constructed withthe optical layers 170 (and support 172) extending over the top of theflange bearing 130 (but without contacting it), so as to increase theoptical fill factor. Otherwise, if the flange bearing is exposed, it maybe desirable to overcoat it with a mask 136, which is provided toprevent a bright back reflection from this surface, which couldotherwise reduce the modulation contrast from the device.

Mask 136 nominally either absorbs or diffusely scatters the incidentlight that falls on it. Similarly, the substructure of modulator 100 mayinclude a light shield 138 disposed on some potentially illuminatedinternal surfaces of micro-motor 105. As with mask 136, light shield 138either absorbs or diffusely scatters the incident light. For highcontrast applications, light absorption would be preferred over lightscattering. Furthermore, both mask 136 and light shield 138 may have amulti-layer structure, comprising for example, an anti-reflection (AR)coating deposited on a light absorbing (nominally black) layer. The ARcoating would be provided to enhance the efficiency of light absorption.Of course, light absorption on significant portions of a spatial lightmodulator 50 constructed with these micro-motors 105 and optical layers170, will cause heating of the packaged device, which could be a problemfor high power applications.

Dimensionally, rotor 160 can be fabricated to be from 60-200 microns indiameter. Stator poles 142 would be approximately 8-20 microns inarcuate length. A nominal clearance (air gap 120) of 2.0 microns wouldbe required between rotor poles 162 and stator poles 142, to permitinteraction between the charged surfaces without having contact.

The design and structure for optical layers 170 of pixel 100 areunderstood with respect to FIG. 5, to form an optic 200 with the desiredpolarization properties. Referring to FIG. 5, there is shown apolarization optical layer 176 which consists of a one dimensionalarrangement of form-birefringent subwavelength optical micro-structures210, which includes grooves 220 and mesas 230. The arrangement ofoptical micro-structures 210 is fabricated into a dielectric material205, in the form of a series of grooves 220 etched or otherwise removedfrom the dielectric material 205, to form a pattern of mesas 230.Depending on the pattern of grooves 220 and mesas 230, as well as thetheir micro-structure (cross-sectional profile), the overall structurecan exhibit form birefringence, and therefore function as a waveplate,providing phase change to an incident light beam. The opticalmicro-structure 210 is characterized by the pitch (p), width (w), andheight or thickness (t) of the mesa/groove structure.

Unlike the bulk birefringence common in optical materials such ascrystals, which is caused by the anisotropic variations in theelectrical properties within the materials, form birefringence is causedby anisotropic patterns of sub-wavelength dielectric structures thatimpart phase changes to the light beam. As is known in the field, a twodimensional pattern of symmetrical dielectric sub-wavelength structures(mesas and grooves) can function similar to an anti-reflection (AR)coating, with a broad wavelength, polarization insensitive, and angleinsensitive response. Such a structure is also known as a “moth's eye”structure, due to its presence in some varieties of moth's. Anasymmetric two dimensional pattern (mesas and grooves different in X andY) can provide a polarization sensitive anti-reflection structure. A onedimensional structure of grooves and mesas, like that of FIG. 5, canprovide an optic with polarization functionality (a polarizationsensitive mirror or a waveplate), as well as exceptional anti-reflectionproperties. As discussed in the paper, “Design considerations ofform-birefringent micro-structures”, by I. Richter et al., (AppliedOptics, Vol. 34, No. 14, pp. 2421-2429, May 1995), the detailed designof optical devices from form-birefringent micro-structures requirescomplex optical modeling. However, the Richter et al. paper alsodiscusses many of the design parameters and compromises involved indeveloping form-birefringent structures, including methods foroptimizing the amount of birefringence.

Relative to use in spatial light modulator 100, the opticalmicro-structures 210 of polarization optical layer 176 can be configuredto fashion optic 200 into a waveplate. For subwavelength operation, thepitch (p) of the micro-structures should nominally be significantly lessthan the wavelength of incident light (p<<λ). However, practicallyspeaking, a pitch of p˜λ/10 provides nearly the optimal performance formost applications, while a pitch p˜λ/4 is sufficiently sub-wavelength togain most of the benefits for most applications, without significantlyencountering any macro-structure optical effects (diffraction). Ingeneral, the phase change or birefringence provided by the opticalmicro-structure 210 can be tuned by controlling the characteristics ofthe groove and mesa structure. The delay (D) provided by the waveplatecan be related to the thickness (t) of the mesas 230, according toequation (1):

t=D*λ/Δn,  (1)

where Δn is the index change (birefringence) provided by the structure.The birefringence for the optical micro-structure of grooves 220 andmesas 230 can be approximated by equation (2);

Δn=n ₇ −n _(⊥)=(w/p+(1−w/p)/n ²)^(½)−(w/p+n ²)*(1−w/p)^(½),  (2)

and the retardation phase change Δφ can calculated by equation (3);

Δφ=2π*t*Δn/λ,  (3)

where n is the nominal index of refraction of the dielectric material205. While the duty cycle (w/p) of the mesa width (w) to the pitch (p)can range from 0.0 to 1.0, optimal performance (maximum phase change orbirefringence) can be found for duty cycles ranging from ˜0.4 to ˜0.6.The theoretical maximum birefringence possible, at a duty cycle of 0.5,for a low index (n=1.46) optical medium such as fused silica, isΔn=0.084.

For the purposes of the design of spatial light modulator 100, it isdesirable that the optic 200 fabricated on micro-motor 105 be a quarterwave plate, and in particular a quarter wave linear retarder. Bycomparison, the nominal maximum retardance, provided by the liquidcrystal layer of a vertically aligned reflective LCD, is also a quarterwave. In this case, using the above equations indicates that to providea quarter wave plate in green light (λ=0.55 μm), the delay (d) is 1/4,the nominal thickness (t) or height of the mesas 230 is ˜1.6 μm, and theretardation phase change Δφ provided is π/2. Assuming this exemplarydevice a pitch p˜λ/4, the nominal width (w) of mesas 230 is ˜69 nm. As aresult, the optical micro-structure 210 for a form-birefringentwaveplate using low index materials (such as SiO₂) requires a largeheight to width aspect ratio (23:1 for this example). With such deepgrooves, device fabrication can be difficult. If a dielectric material205 with a larger refractive index (n) can be used, the index change(Δn) from the form birefringence is larger, and the groove depth can bereduced for the same delay (D).

While the mesas 230 of FIG. 5 are illustrated as having a rectangularprofile, it should be understood that other profiles are possible, andin some cases, advantageous. In particular, gradually tapering ortriangular structures will provide improved transmission (lowerreflectivity), but also less phase change. Depending on the desireddesign, exchanging increased efficiency for reduced phase change may beacceptable. In general, these form birefringent optical micro-structures210 which define optic 200 as a waveplate, provide a uniform response(nearly constant retardance) for the incident light over a large rangeof incident angles (˜+/−20°).

In addition to the polarization optical layer 176, the optical layers170 of pixel 100 also include a reflective layer 174. In operation, theincident light passes through polarization optical layer 176, and gainsthe appropriate phase change in accordance with the design of theoptical micro-structure 210, and the rotational position of the devicerelative the polarization state of the light. The light than reflectsoff reflective layer 174, and passes through polarization optical layer176, thereby gaining additional phase change. The reflective layer 174can either be a thin metallic coating, or a multi-layer dielectric highreflectance (HR) coating, as long as it provides a high reflectivity andlow scatter. In order to minimize fabrication process steps, reflectivelayer 174 is most likely a coated metal layer. The thickness of thismetal layer is nominally required to be at least as thick as the skindepth (δ). Incident light is considered to only propagate through ametal film only a short distance, known as the skin depth (δ), beforereflection occurs. Skin depth can be calculated by equation (4) asfollows:

δ=λ/4πn _(i),  (4)

where the calculated depth corresponds to the distance at which thelight intensity has decreased to ˜1/e² of its value at the input surface(where n_(i) is the imaginary part of the refractive index).Traditionally, thin metal layers are considered opaque relative totransmitted visible light when their thicknesses exceed the typical skindepth (δ) values, which for metals such as aluminum or silver, are only10-15 nm.

Referring to FIGS. 6a and 6 b, there is shown how rotation of optic 200,mounted to micro-motor 105, provides modulation for light that isdirected to a single pixel 100. Depending on the rotation of themicro-motor, the local polarization axis 245 of optic 200 may be alignedparallel to the system polarization axis 240, perpendicular to it, or atsome intermediate angle (shown as α in FIG. 6a, or β in FIG. 6b). Thesystem polarization axis 240 may correspond to the OFF state (if thepolarization beam splitter 30 and polarization analyzer 35 are crossed)or the ON state (if the polarization beam splitter 30 and polarizationanalyzer 35 are aligned).

The transmitted polarized light beam 40 encounters the optical layers170, shown in FIG. 5, of optic 200, including the dielectric material205 with its pattern of optical micro-structures 210, and reflectivelayer 174. Optic 200 is nominally a quarter wave linear retarder plate,which polarized incident light beam 40 encounters twice (both before andafter reflection from reflective layer 174) in the process of becomingmodulated light beam 55. As a result, if optic 200, is constructed as aquarter wave plate, it functions as a halfwave plate. This means thatwhen its local optical axis is 245 located at 45° relative to the systemoptical axis 240, the polarization state of the polarized incident lightbeam 40 can be rotated a full 90° (from On State to Off State, forexample). FIG. 6a shows this case, where angle α corresponds to 45°.FIG. 6b shows another case, where the optic 200 is rotated to anintermediate angle β. When polarized incident light beam 40 encountersoptic 200 at an intermediate angle, the rotation of the polarizationstate will be partial, and the resulting light will be ellipticallypolarized. When this modulated light beam 55 then encounters thepolarization analyzer 35 of modulation optical system 10, the intensityof the transmitted light will emerge at an intermediate level dark andlight (Off and On), thus providing intermediate levels of brightness forthe corresponding pixel.

Strictly speaking, it is not required that when optic 200 is a retardingwaveplate, that it be constructed as a quarter wave plate. For example,optic 200 could have 1¼ waves of retardance and still function in thesame manner. However, as the aspect ratio (height to width) of mesas 230(or groove depth) would greatly increase, this is not advantageous.Alternately, optic 200 could be a half-wave plate (effectively a fullwave plate with the reflection) and operate in a similar manner, butthen the gray scale resolution (ability to hit intermediate brightnessvalues) would likely be reduced.

Gray scale resolution also depends on the discrete rotational resolutionof micro-motor 105, as a function of the number and positioning ofstator poles 142 and rotor poles 162 and of drive signal phasing. As isdisclosed in U.S. Pat. No. 5,909,069 (Allen et al.), a three-phasedevice having twelve stator poles 142 and ten rotor poles 162 wouldprovide 30 steps per rotation, at 12 degrees per step. This correspondsto only 15 discrete steps or levels from one on-state to the nexton-state, or ˜8 steps from on-state to off-state. By using drive signalphase control, the micro-motor may be driven to intermediate rotationalpositions, which do not correspond to precise rotor to stator alignment,thereby increasing the number of steps per rotation. The actual minimumstep size will then depend on the dynamics of the micro-motor and thesophistication of the drive signal phase control.

Unlike many of the other suggested applications for micro-motors wherethe motors operate at speed for a period of time, in this application,where micro-motor 105 enables the construction of a micro-mechanicalpolarization light modulator, the operational conditions require acontinuing series of rapid accelerations and de-accelerations. FIG. 9 ofU.S. Pat. No. 6,029,337 provides one example of a step response for aloaded micro-motor, where the device can rotate through 15° in ˜1 msec.It is then realistic to anticipate that the device of the presentinvention can be operated as a polarization modulator with responsetimes of a few msec per step. Actuation times could decrease if eachpixel 100 of the device (spatial light modulator 50) could be drivenbi-directionally rather than uni-directionally. Actuation times couldfurther decrease if it is not required to drive the pixels past areference position, such as an on state or off state position, to getfrom one gray scale code to another.

In general, the invention provides a spatial light modulator havingmodest pixel resolution and a fill factor approaching 75%. Gray scaleresolution may be somewhat limited, depending on the number ofcontrollable steps per rotation. However, the apparatus of the presentinvention provides a favorable response time and uniform angularresponse over a large range of incident angles.

There are a number of alternatives for mechanical actuation of themicro-motor 105. These include configurations using an outer rotor,magnetic micro-motors such as is disclosed in U.S. Pat. No. 5,710,466(Allen et al.), and other devices.

There are also alternate approaches for designing the optical layers 170of the micro-mechanical polarization modulator. For example, the designof spatial light modulator array 50 can be constructed to provide anoptic 200 with polarization altering optical structures other thansub-wavelength form-birefringent wave plates. In particular, FIG. 7shows a basic prior art visible wavelength wire grid polarizer asdiscussed in U.S. Pat. No. 6,122,103. The wire grid polarizer 300 iscomprised of a multiplicity of subwavelength parallel conductiveelectrodes (wires) 310 with separating grooves 220 supported by adielectric substrate 320. This device is characterized by the gratingspacing or pitch or period of the conductors, designated (p); the widthof the individual conductors, designated (w); and the thickness of theconductors, designated (t). Nominally, a wire grid polarizer usessub-wavelength structures, such that the pitch (p), conductor or wirewidth (w), and the conductor or wire thickness (t) are all less than thewavelength of incident light (λ). A beam of light 345 produced by alight source 340 is incident on the polarizer at an angle θ from normal,with the plane of incidence orthogonal to the conductive elements. Thewire grid polarizer 300 divides this beam into specular non-diffractedoutgoing light beams, including reflected light beam 350 and transmittedlight beam 355. The definitions for “s” and “p” polarization used arethat “s” polarized light is light with its polarization vector parallelto the conductive elements, while “p” polarized light has itspolarization vector orthogonal to the conductive elements. In general, awire grid polarizer will reflect light with its electric field vectorparallel (“s” polarization) to the grid, and transmit light with itselectric field vector perpendicular (“p” polarization) to the grid. Wiregrid polarizer 300 is a somewhat unusual polarization device, in that itis an E-type polarizer in transmission (transmits the extraordinary ray)and O-type polarizer in reflection (reflects the ordinary ray). The wiregrid polarizer does not quite fit the definition of a form-birefringentstructure, as one refractive index is imaginary.

When such a device is used at normal incidence (θ=0 degrees), thereflected light beam 350 is generally redirected towards the lightsource 340, and the device is referred to as a polarizer. However, whensuch a device is used at non-normal incidence (typically 30°<θ<60°), theilluminating beam of light 345, the reflected light beam 350, and thetransmitted light beam 355 follow distinct separable paths, and thedevice is referred to as a polarization beamsplitter. The detaileddesign of a wire grid device, relative to wire pitch (p), wire width(w), wire duty cycle (w/p), and wire thickness (t), may be optimizeddifferently for use as a polarizer or a polarization beamsplitter.

A typical wire grid polarizer 300 used for visible wavelengthapplications, as manufactured by Moxtek Inc. of Orem UT, hassubwavelength wires 310 with a wire pitch (p) of ˜140 nm, or ˜λ/4 forvisible light. The typical device also has a wire duty cycle (w/p) of˜0.5, and a wire thickness (t) of 100-200 nm. This means that the wirethickness to wire width aspect ratio is a modest ˜2:1. The dielectricsubstrate 320 is typically aborofloat glass of ˜0.8 to 3.0 mm thickness.Wires 310 are nominally metallic, and may be constructed with aluminum,silver, gold, nickel, or chrome (for example). While the transmittedcontrast (Tp/Ts) can be very high (1,000:1 or more), the reflectedcontrast (Rs/Rp) is relatively low (˜30:1).

Accordingly, the micro-mechanical polarization modulator can beconstructed as shown in FIG. 8 with an optic 200 using a polarizationoptical layer 176 with an optical micro-structure 210 constructed as awire grid polarizer with wires 310 and grooves 220. This is in contrastto the prior example, where optic 200 had a polarization optical layer176 that formed a waveplate with a dielectric optical micro-structure210 as was shown in FIG. 5. In this instance, where the optic 200 formodulator 100 is a wire grid polarizer, the polarization optical layer176 comprises the pattern of parallel electrically conductive wires 310fabricated on a dielectric layer 180. The optical layers 170 thencomprise both polarization optical layer 176 and a light absorbing layer184, both of which are fabricated on support 172. In accordance withmost deposition processes, the dielectric layer 180 of the polarizationoptical layer 176 may only be many (5-100) microns thick, as compared tothe ˜1.0 mm substrate thickness of the typical macro-optical wire gridpolarizer. Considering the description of the operation of a standardwire grid polarizer 300, relative to FIG. 7, the equivalent to the “p”polarized transmitted light beam 355 is absorbed by light absorbinglayer 184 in optic 200 of FIG. 8. Obviously, the heat generated by thislight absorption can cause problems unless it is properly removed fromthe device. However, when optic 200 is a wire grid polarizer, ratherthan a wave plate retarder, the angular resolution (gray scale control)should be increased, as there will be twice the number of potentialsteps from On State to Off state.

Although the two structures, where optic 200 is a waveplate (FIG. 5),and where optic 200 is a wire grid polarizer (FIG. 8) look similar, theyare actually quite different. The fact that wire grid polarizer useswires 310 made as thin metal strips, vs. the optical micro-structures210 made with thin dielectric strips, means that the optical responsemechanisms are fundamentally different, as the wire grid device is apolarizer, while the waveplate is a retarder. Additionally, the actualmicro-structures are optimized differently, relative to the groove depth(t) and other parameters.

In addition, the construction of a modulation optical system 10 using aspatial light modulator array 50 with modulators 100 constructed with anoptic 200 that is a polarizer (such as a wire grid polarizer) isdifferent than the prior case where optic 200 is a waveplate. When optic200 is a waveplate, it is ideal if polarization beamsplitter 30transmits one polarization (typically “p”) while reflecting the other(typically “s”). However, when optic 200 is a polarizer, modulationoptical system 10 is, for example, constructed as shown in FIG. 1b,without a polarization beamsplitter, but with the polarized incidentlight beam 40 introduced from off-axis, and with the modulated lightbeam 55 exiting also at a nominally non-normal angle. In this case, thetypically large acceptance angle (+/−20° or more) of the wire gridpolarizer, means that modulation optical system 10 can be constructed inthis fashion, while still allowing relatively fast optical systems.

Notably, as discussed in commonly-assigned copending U.S. patentapplication Ser. No. 09/799,281, filed Mar. 5, 2001, entitled WIRE GRIDPOLARIZER, by Kurtz et al., a resonance enhanced tunneling effect can beused to design a better wire grid polarizer. In particular, as discussedin the paper “Transparent, Metallo-Dielectric, One-Dimensional, PhotonicBand-Gap Structures” in J. App. Phys. 83 (5), pp. 2377-2383, Mar. 1,1998, by M. Scalora et al., a photonic bandgap structure can be designedusing an optical micro-structure comprising a stratified arrangement ofthin metal layers and thin dielectric layers, such that resonanceenhanced tunneling dramatically increases the transmission through themetal layers, even if these layers are several skin depths thick. In theScalora paper, this effect is used to provide enhanced lighttransmission within prescribed optical bandpass regions, while the otherwavelengths are blocked. But as discussed in the above application, thisconcept can be extended to the design of a broad wavelength wire gridpolarizer which provides enhanced contrast.

This alternate concept for a wire grid polarizer 300 is shown in FIG. 9,in which the sub-wavelength wires 310 are constructed on a dielectricsubstrate 320 with a stratified intra-wire substructure 370 comprisingalternating metal layers (372, 374, and 376) and dielectric layers (380,382, and 384). Resonance enhanced tunneling of “p” polarized lightthrough the stratified structure of thin dielectric and thin metallayers shown in FIG. 9 increases the transmission (Tp) for this light.However, the reflection of the “s” polarized light (Rs) can also beincreased. As a result, the use of a stratified intra-wire substructure370 comprising alternating metal layers (372, 374, and 376) anddielectric layers (380, 382, and 384) can cause both the transmitted(Tp/Ts) and reflected (Rs/Rp) contrasts to increase. The number,thickness, and order of the various metal layers and dielectric layerscan be adjusted to optimize the performance.

This same concept can be adapted for use in modulator 100, byconstructing the wires 310 of optical micro-structure 210 within optic200 as a polarizer with a stratified wire structure using the intra-wiresubstructure 370 of FIG. 9. Of particular significance for modulator100, is the ability of the stratified wire structure to significantlyenhance the reflected contrast (to 200:1 or greater). As previously,with regards to FIG. 8, a polarization optical layer 176 is providedwith an optical micro-structure 210 as a combination of (stratified)wires 310, separating grooves 220, and a dielectric layer 180. Thestratified wires 310 are fabricated on the dielectric layer 180, whichis in turn fabricated on light absorbing layer 184 and support 172.

As yet another alternative for providing the optic 200 for modulator100, the paper “Design, fabrication, and characterization ofform-birefringent multilayer polarizing beam splitter,” by R. Tyan etal., and published in JOSA A, vol. 14, no. 7, pp. 1627-1636, July 1997,discusses a useful concept for a form-birefringent polarizer. The Tyandevice is in some ways physically similar to the wire grid polarizer 300of FIG. 9, which has the sub-wavelength wires 310 constructed on adielectric substrate 320, with a stratified intra-wire substructure 370comprising alternating metal layers (372, 374, and 376) and dielectriclayers (380, 382, and 384).

However, in the Tyan device, the equivalent to the metal layers 372,374, and 376 are not metallic, but are dielectric layers with differentproperties from dielectric layers 380, 382, and 384. The Tyan devicealso functions as a polarizing beam splitter, reflecting “s”polarization, while transmitting “p” polarization. The device of theTyan paper was optimized for use in the near infrared (˜1.5 μm), ratherthan in the visible. While the concept is presumably extendable to thevisible wavelength region, the required thickness (t) and aspect ratiosof the optical micro-structures would increase, making fabricationcomparatively more difficult. Moreover, the polarization contrast,wavelength response, and angular acceptance are significantly morelimited than the equivalent wire grid device.

It may also be possible that optic 200 can be constructed with apolarization optical layer 176 that does not utilize a opticalmicro-structure 210, such as the waveplate/retarder of FIG. 5, or thewire grid polarizer of FIG. 8. Of course, any alternate method forproviding polarization optical layer 176 should lend itself tofabrication methods compatible with miniaturization and patterning. Inparticular, it may be possible to provide polarization optical layer 176as a properly designed polarization sensitive optical thin film coating.It is however difficult to obtain significant polarization differencesin transmission or reflection over a large wavelength band at normalincidence with optical thin film coatings. Such an alternate approachmay have better success if the optic 200 is used on spatial lightmodulator array 50 within a modulation optical system 10 of the sortshown in FIG. 1b, where the polarized incident light beam 40 is incidentat non-normal incidence. It would not be expected that such a devicewould have as uniform a response with angle as the equivalent devicewith an optical micro-structure 210.

The invention has been described in detail with particular reference tocertain preferred embodiments thereof. It will be understood, however,that variations and modifications can be effected within the scope ofthe invention as described above, and as noted in the appended claims,by a person of ordinary skill in the art without departing from thescope of the invention. For example, although a spatial light modulatorhaving a plurality of modulators (or pixels) is described, a device witha single pixel comprised of a micro-mechanical actuator with anintegrated polarization modulation means may be useful in certainapplications. In addition, although the term micro-motor has beendescribed as being comprised of a rotor and a stator, other types ofmicro-mechanical actuators may be employed in the invention. Forexample, actuators that extend and contract to rotate the polarizationoptical layer to different positions, or use levers or micro-gearmechanisms, are all within the scope of the invention. Likewise, itshould be understood that while the discussion of the use and design ofthe spatial light modulator has focused on optimization for use in thevisible wavelength region, the concepts are applicable to otherwavelength bands, and are particularly realizable in the near infra-redspectrum.

PARTS LIST

10. Modulation optical system

20. Incident light beam

21. Polarized light beam

25. Pre-polarizer

30. Polarization beamsplitter

32. Polarizing filter layer

35. Polarization analyzer

37. Reflected light beam

40. Transmitted polarized incident light beam

50. Spatial light modulator array

51. Drive signal

55. Modulated light beam

70. Projection lens

100. Modulator or pixel

105. Micro-motor

110. Substrate

112. Intermediate layer

120. Air gap

130. Flange bearing

132. Lower flange

134. Upper flange

136. Mask

138. Light shield

140. Stator

142. Stator pole

144. Stator lead

160. Rotor

162. Rotor pole

164. Ground plane

166. Insulating layer

170. Optical layers

172. Support

174. Reflective layer

176. Polarization optical layer

180. Dielectric layer

184. Light absorbing layer

200. Optic

205. Dielectric material

210. Optical micro-structure

220. Groove

230. Mesa

240. System polarization axis

245. Local polarization axis

300. Wire grid polarizer

310. Parallel conductive electrodes (wires)

320. Dielectric substrate

340. Light source

345. Beam of light

350. Reflected light beam

355. Transmitted light beam

370. Intra-wire substructure

372. Metal wire

374. Metal wire

376. Metal wire

380. Dielectric layer

382. Dielectric layer

384. Dielectric layer

What is claimed is:
 1. A micro-mechanical spatial light modulator formodulating a polarization state of an incident beam comprising: aplurality of rotatable elements, wherein each of said rotatable elementcomprises an optic with a polarization optical layer; wherein each ofsaid polarization optical layers are comprised of a plurality of opticalmicro-structures fabricated in a pattern with features spaced apartwithin sub-wavelength distances relative to a wavelength of saidincident beam, wherein each of said plurality of structures interactswith said polarization state of said incident beam; a plurality ofmicro-motors coupled to each of said rotatable element, wherein saidmicro-motors are capable of controllably positioning said rotatableelement to any of a plurality of positions, wherein each of saidpositions has a corresponding polarization state; wherein each of saidpolarization optical layers, are formed on said micro-motors; and asubstrate for supporting each of said plurality of rotatable elementsand said micro-motors.
 2. The spatial light modulator of claim 1 whereineach of said micro-motors comprises a stator with a series of statorpoles and a rotor with a series of rotor poles.
 3. The spatial lightmodulator of claim 2 wherein said polarization optical layers are formedon top of each of said rotors.
 4. The spatial light modulator of claim 2wherein a mask covers an upper flange of a flange bearing of each ofsaid rotors.
 5. The spatial light modulator of claim 4 wherein said maskabsorbs light.
 6. The spatial light modulator of claim 4 wherein saidmask scatters light.
 7. The spatial light modulator of claim 1 whereineach of said micro-motors is moved electrostatically.
 8. The spatiallight modulator of claim 1 wherein said optic, including saidpolarization optical layer, overhangs a rotor and a stator of saidmicro-motor.
 9. The spatial light modulator of claim 1 wherein a lightshield covers portions of internal surfaces of said micro-motor whichmight otherwise reflect light in an undesirable manner.
 10. The spatiallight modulator of claim 9 wherein said light shield absorbs light. 11.The spatial light modulator of claim 9 wherein said light shieldscatters light.
 12. The spatial light modulator of claim 1 wherein: eachof said polarization optical layers exhibits form birefringence andfunctions as a waveplate, providing a known retardation phase change;and a reflective layer located beneath each of said polarization opticallayers.
 13. The spatial light modulator of claim 12, wherein saidwaveplate is a quarter wave plate.
 14. The spatial light modulator ofclaim 12, wherein said optical layers are optimized for operation in thevisible spectrum.
 15. The spatial light modulator of claim 12 whereinsaid structures are spaced apart at a pitch of p˜λ/4 or less.
 16. Thespatial light modulator of claim 1 wherein: said polarization opticallayers comprise a wire grid polarizer with a pattern of alternatingwires and grooves; and light absorbing layers are located beneath saidpolarization optical layers.
 17. The spatial light modulator of claim16, wherein wires comprising said wire grid polarizer comprise astratified substructure of alternating metal and dielectric layers. 18.The spatial light modulator of claim 16 wherein said structures arespaced apart at a pitch of p˜λ/4 or less.
 19. A micro-mechanical spatiallight modulator for modulating a polarization state of an incident beamcomprising: a rotatable element supporting an optic with a polarizationoptical layer, said polarization optical layer comprising a plurality ofoptical micro-structures fabricated in a pattern, wherein said opticalmicro-structures are spaced apart at sub-wavelength distance relative toa wavelength of said incident beam, wherein said opticalmicro-structures exhibits an interaction with said polarization state ofsaid incident beam; and a micro-motor coupled to said rotatable element,said micro-motor capable of controllably positioning said rotatableelement to any of at least two positions, wherein each of said positionshas a corresponding polarization state.
 20. The spatial light modulatorof claim 19 wherein said polarization optical layers are formed on topof rotors of said micro-motor.
 21. The spatial light modulator of claim19 wherein: said optical micro-structures exhibit form birefringence andfunction as a waveplate, providing a known retardation phase change; anda reflective layer located beneath each of said structures and attachedto rotors of said micro-motor by means of a support.
 22. The spatiallight modulator of claim 17 wherein: said optical micro-structurescomprise a wire grid polarizer with a pattern of alternating wires andgrooves; and a light absorbing layer is located beneath each of saidstructures and attached to a rotor of said micro-motor by means of asupport.
 23. A micro-mechanical spatial light modulator for modulating apolarization state of an incident beam comprising: a plurality ofmicro-motors each comprised of a rotor and a stator; a plurality ofoptical elements each of which is mounted on each of said rotors,wherein each of said optical elements comprises a plurality of spacedapart sub-wavelength optical micro-structures, wherein said opticalmicro-structures are fabricated in a pattern; and a driver whichprovides a signal to each of said micro-motors which causes each of saidmicro-motors to rotate to a plurality of positions.
 24. The spatiallight modulator of claim 23 wherein said optical elements are formed ontop of said rotors.
 25. The spatial light modulator of claim 23 wherein:said optical micro-structures exhibit form birefringence and function asa waveplate, providing a known retardation phase change; and areflective layer located beneath each of said optical elements attachedto said rotor by means of a support.
 26. The spatial light modulator ofclaim 23 wherein: said optical elements comprise a wire grid polarizerwith a pattern of alternating wires and grooves; and a light absorbinglayer located beneath each of said optical elements and attached to saidrotors by means of a support.
 27. A spatial light modulator as in claim23 wherein each of said plurality of optical elements interacts withsaid polarization state of said incident beam in relation to an amountof rotation of said optical element.
 28. A micro-mechanical spatiallight modulator for modulating a polarization state of an incident beamcomprising: a plurality of rotatable elements wherein each of saidrotatable element comprises an optic with a polarization optical layer;wherein said polarization optical layer, comprising opticalmicro-structures fabricated in a pattern, interacts with saidpolarization state of said incident beam; a micro-motor is coupled toeach of said rotatable element, said micro-motor capable of controllablypositioning said rotatable element to any of a plurality of positions,wherein each of said positions has a corresponding polarization state;wherein each of said polarization optical layers are formed on saidmicro-motor; and a substrate for supporting each of said plurality ofrotatable elements and for housing each of said micro-motors.
 29. Amicro-mechanical spatial light modulator for modulating a polarizationstate of an incident beam comprising: a plurality of rotatable elements,wherein each of said rotatable elements comprises an optic with apolarization optical layer; wherein each of said polarization opticallayers are comprised of a plurality of optical micro-structures spacedapart within sub-wavelength distances relative to a wavelength of saidincident beam, wherein said optical micro-structures are fabricated witha defined pitch, width, and thickness, and wherein each of saidplurality of optical micro-structures interacts with said polarizationstate of said incident beam; a plurality of micro-motors coupled to eachof said rotatable element, wherein said micro-motors are capable ofcontrollably positioning said rotatable element to any of a plurality ofpositions, wherein each of said positions has a correspondingpolarization state; wherein each of said polarization optical layers,are formed on said micro-motors; wherein each of said micro-motorsrotates between at least a first and second position to modulate saidincident beam; and a substrate for supporting each of said plurality ofrotatable elements and said micro-motors.